BD+40°4210 is a hot luminous supergiant star located in the constellation Cygnus. It is a member of the Cygnus OB2 association and a candidate luminous blue variable.
==Features== BD+40°4210 is heavily reddened and extinguished by the interstellar dust of the Milky Way and little studied. It has turned out to be one of the most luminous stars of the Cygnus OB2 association, with an absolute magnitude of −7.66 and a bolometric luminosity more than 600,000 times that of the Sun. It has been assigned a B1III spectral classification, but with peculiarities including unusually shallow lines and broad emission. Despite the giant luminosity class, the luminosity appears to be extremely high, placing it on or near the S Doradus instability strip occupied by quiescent luminous blue variables. Its brightness varies by less than 0.1 magnitudes on a timescale around 100 days.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).